This invention relates to clamping bands for cylindrical objects and in particular to a metal band which is apertured to have an extremely high degree of stretch about its circumference.
Metal bands have been used for hose clamps and similar applications wherein it is desired to secure an elastomeric member to a rigid part or to apply compressive force to a resilient object for any number of applications. In certain of these applications, it is desired that the band be automatically readjusted or retighened during use to accommodate changed conditions and it is desirable to have a certain degree of spring in the band to automatically achieve this end.
For example, with respect to a metal clamp of this type for securing hose to a nipple or the like, it is desirable that the clamp accommodate pressure pulsations which occur in the fluid system without incurring permanent plastic deformation and yet retain the hose affixed to the nipple. Upon aging of the hose it is common for the elastomeric material of the hose to take a permanent set and it is desirable as well that the metal clamp continue to exert effective clamping force even though such altered dimensions and characteristics of the hose are encountered. Still further, it is desired that the hose clamp can be readily removed and repositioned upon the hose for service or maintenance purposes and that adjustable tensioning or dimensioning of the hose clamp be readily available. Still further, it is desired to have the clamp accommodate itself to the enlarging and shrinking of hoses and nipples which occur due to thermal expansion. This thermal expansion can be due to temperature changes in the fluid system or ambiant conditions.
Another application for a clamping band is to secure an elastomeric dust cover to a drive shaft or the like. This application is considerably different in that the underlying structure is relatively inelastic and any continuing clamping force must be derived substantially from the band clamp itself. It is further apparent, that if resilience in the combined structure is required in order to engage the ends of the clamp, such resilience must be provided substantially wholly by the clamp, and still retain its spring-like characteristics, once installed.
Several situations occur wherein it is desired to have a clamp which exhibits the characteristics of a permanent, plastic stretch and that of a temporary, elastic stretch. One situation is where there is no screw tightening means for the clamp but where it is tensioned using an external tool with the tension "locked" into the band by latching up a pawl or hook to a set of teeth or projections or the like. In such an application the elastic stretch would allow the retention of a known portion of the band load induced by the tool, after the slackening off that occurs when the pawl passes over the top of a tooth and comes to full engagement at the circumferentially displaced bottom of that same tooth.
In another application, previously described, wherein it is desired to place the clamp about an inelastic body and make use of the hook and tooth locking arrangement, it will become apparent that the teeth cannot be made small enough and still be structurally sound to allow an external tightening tool to bring a proper tension into the relatively rigid prior art clamping bands. In such application, there is insufficient stretch in the band to allow makeup with adjacent teeth and the item being clamped does not compress sufficiently to allow the pawl to reach the next tooth.
As noted, the elastic stretch capability in a band is particularly helpful in the application wherein the item being clamped expands or contracts, such as in a hose clamp. Here an elastic band follows the expansions and contractions of the object and maintains the seal without incurring permanent distortion.
A number of clamps are already known which utilize the advantage of including some degree of resilience for certain of the reasons enumerated above. One such example is shown in U.S. Pat. Nos. 3,475,793 and 3,523,337. Here the band includes a plurality of tensional spring elements in the form of ear-shaped folds which are distributed over the circumference of the band. A pawl and tooth type band closing mechanism is employed permitting a step-like fitting of the band to an object to be clamped. This type of clamp is limited in requiring substantial radial space to accommodate the spring portions of the band and requires a relatively complicated forming operation during manufacture whereby bending of the metal strip must be performed in a plurality of locations. It is also limited to low tension loads and high spring rates (i.e. high values of inches per pound inch).
A similar form of hose clamp is described in U.S. Pat. No. 4,308,648 wherein a series of convolutions of the metal strip are provided at one location in the circumference of the band to provide a desired amount of resilience to the band. This arrangement is subject as well to the radial space limitation and requires effecting multiple bends in the strap during manufacture. This clamp also discloses an inner shield beneath the convoluted area to prevent extrusion of the elastomeric material of the hose into the convolutions which would affect the resilience of the clamp. Such device is a separate component in the embodiments described and requires some form of attachment to the remainder of the clamp.
Another form of prior art hose clamp is shown in U.S. Pat. No. 1,705,895 wherein a metal band is shaped in at least one portion thereof in a dual zigzag pattern and provided with a hook and ratchet tooth type fastener for closing the ends of the clamp. The zigzag portion is utilized to provide resilience or springiness to the clamp to accommodate the compression set of underlying hose structures and the like and is described as bending slightly under tension to provide the springiness. It is this type of hose clamp with which the instant invention is concerned whereby improved results and manufacturing efficiencies are to be achieved. The hose clamp shown in this patent teaches primarily that the resilience is provided to account for compression set in the hose and shows a localized treatment of the subject at one or two locations about the circumference. Further, the sharp zigzag configuration is not well suited for large elastic excursions without incurring plastic deformation and is not an efficient utilization of the metal material.
Still another form of clamp or connector strap is shown in U.S. Pat. No. 3,324,234, this being a metal strip which is punched or otherwise shaped to provide a configuration throughout the circumference of the strap of a series of transversely extending spring arms. Each arm terminates in radially inwardly bent legs which are adapted to engage the object to be clamped. When the center portion of the strap is drawn taut for securement, the spring arms are depressed at the center to provide a resilient force. The center portion of the strap includes a plurality of transversely extending slots in each spring arm to receive the connecting tab. This form of strap is designed primarily for engagement with substantially rigid objects and to provide both a mechanical and an electrical connection therewith.